Signal storage tubes



April 20, 1965 E. B. B. cALLlK ETAL 3,179,833

SIGNAL STORAGE TUBES Filed Feb. 2l, 1961 llllllixlllll lllll Il llllllllll lllll ATTORNEYS United States Patent O s cams. (c1. 31a-7i) Thisinvention relates to signal storage tubes and more particularly toso-called direct View storage tubes of the kind wherein a charge image,corresponding to applied signals and formed on a storage electrode bymeans of an electron beamfrom a writing electron gun, is used tomodulate the electron beam of a ood electron gun, the modulated beamimpinging on a iiuorescent screen and displaying thereon an imagecorresponding to the stored charge image.

Such tubes as at present known Sutter from the defect that one of thetwo electron guns-more usually the writing gunis considerably offsetfrom the tube axis so that its electron beam meets the storage electrodeat an angle which is far from a right angle, with the result thatundesired shading and distortion of the finally displayed image takesplace. Furthermore, these known tubes suffer from the additional defectsthat they require undesirably great care in design and construction toensure that the flooding beam is uniformly distributed over the storageelectrode and that they require the use of a high voltage writing gun toobtain high resolution.

It is the object of the present invention to provide improved storagetubes which are free of the above mentioned defects. i

According to this invention the Hood electron gun` of a signal storagetube of the kind referred to is positioned between the writing electrongun and the storage electrode and is so constructed as to providepassage therethrough for the electron beam of said writing gun.Preferably said flood and writing guns are co-axial.

Preferably the cathode ot the ilood gun comprises a grid or mesh ofelectron emissive material which may be directly or indirectly heated.In one construction in which the said cathode is directly heated, itcomprises an array of heater wires coated with electro-emissivematerial.

Preferably there are means for providing a collimating immersinglongitudinal (axial) magnetic iield for said storage tube. l

A preferred form of storage tube arrangement in accordance with thisinvention comprises a storage tube having, in the order stated, awriting electron gun mounted on the` axis of said tube and adapted toproduce, in operation, a substantially cylindrical writing electronbeam, a iiood electron gun co-axial with said writing gun and having acathode comprising a grid 'or mesh of electron emissive materialemitting the electrons forming the flood beam, `said grid or mesh havinga high ratio of space `to conductor width, a secondary electroncollector electrode mounted in a plane perpendicular to said axis, astorageelectrode parallel to, and closely spaced from, saidcollectorelectrode and comprising a metallic grid or mesh havingdeposited thereon on the side nearer the collector electrode a layer ofinsulating material, and a `fluorescent screen arranged parallel to saidstorage electrode; means for applying signals to be stored to modulatesaid writing beam; means, intermediate said writing and iiood guns, fordeiiecting said Writing beam; and ymeans for applying a collimatingimmersing axial magnetic eld to said tube. Preferably said tube includesan accelerating mesh arranged does, comprise a gun system of the kindcommonly used.'

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parallel to and closely spaced from said storage electrode on the sidethereof nearer the fluorescent screen.

The invention is further described with reference` to the accompanyingdrawing, the single ligure of which shows, in simplified diagrammaticform, one embodiment thereof.

Referring to the drawing, 1 is the envelope of an electron dischargestorage tube having on one end face, which is perpendicular to the tubeaxis, a liuorescent screen 2 having a metallic backing film (notseparately.

shown). Parallel to the screen 2 but spaced therefrom is a storageelectrode which is well known, and cornprises a metal grid 31 havingdeposited, on the side remote from the fluorescent screen 2, adielectric layer 32 which is so formed as to leave the interstices ofthe supporting grid 31 open.

Closely adjacent the storage electrode 3 but spaced therefrom are twometal meshes, one on each side, the mesh 4 being arranged to operate asa secondary electron collector and the mesh 5 as an acceleratingelectrode. The provision of the accelerating mesh 5 is in accordancewith the invention described in British Patent No. 890,627 and,accordingly, the spacing between the uorescent screen 2 and the storageelectrode 3 is in excess of that which is common in known storage tubes.Although the use of the accelerating electrode 5 is preerred, it is notanecessity, and if desired it may be dispensed with and the storageelectrode 3 arranged closely adjacent the iluorescent screen 2 in knownmanner.

g At the opposite end of the tube from the iiuorescent screen is thewriting electron gun 6 which is arranged on the tube axis and which maybe as known per se. This gun is arranged .to produce a Writing electronbeam which is substantially cylindrical and of small cross-sectionalarea. Thus the electron gun 6 may, and as shown,

in the Vidicon tube.` The electron gun also includes means, which forsimplicity are` notrseparately shown, for accelerating the electronstherefrom. and for modulating the electron beam in accordance withappliedrsignals.

At the neck of the tube is provided a flood electron` arrangement theheater Wires are mounted in zig-Zag fash-` ion on` an annular mica mountwhich is fitted concentri-` cally in the neck of the tube. The anode 72is a metallic mesh which is also of high transparency and is mountedparallel to and spaced from the cathode 71.

The coils 8 and 9 provide an immersing, `so-called bottle-shaped, axialmagnetic iield, which is so arranged that its iiux density at any pointalong the length of the tube is approximately inversely proportional-tothe crosssectional area of the tube at that point. `Furthermore thelines of force of this eld are arranged to be substantiallyperpendicular to the planes of the flood gun 7,`

the storage electrode 3 and the fluorescent screen 2, and at theseplanes `the iield is arranged to be homogeneous and the above mentionedrelation between the flux density and the cross-sectional area isobtained.

In operation the flood gun 7 isV arranged 'to be con-A tinuously on, thecathode '71 producing flood beam electrons which are drawn ott by thepositive potential applied to the anode 72 and a space charge is formedbetween the anode 72 and cathode 71. In consequence the electronsemanating from the gun 7 are substantially y Patented ApiudZO, 1965Vorthogonally.

The writing7 electron beam is aligned on the axis of the tube by thealignment coil l@ and is deflected by means of a coil system representedby the coil 1l in any suitable kmanner, they beam being modulated inknown manner in accordance with signals to be stored and re-V produced.Due to the high transparency of the flood gun 7 and the negativepotential at which the writing gun cathode is held in operation relativeto the iood gun cathode, the Writing beam passes freely therethrough, isdirected and focussed by the immersing magnetic iield, and strikes thestorage electrode 3 orthogonally.

' The velocity of the writing beam on striking the storage electrode isarranged to be such as to cause the ratio of secondary electrons toprimaryr electrons to exceed unity. The secondary electrons arecollected by the collector mesh 4, which is maintained at a suitablepositive potential,` and the storage electrode accordingly stores apositive charge image which is representative of the signal applied tomodulate the writing beam. The positive charge image on the storageelectrode modulates the vfiooding beam causing it to pass through thestorage electrode, to be accelerated by the accelerating mesh 5, andthen to strike the screen 2, thus producing a picture representative ofthe stored image. This action of storage on the storage electrode andreproduction of the applied signals therefrom is well known per se andac cordingly does not require further description here.

The dimensions of the tube, the strength of the immersing magnetic lieldand the potentials applied to the tube electrodes are all arranged to besuch that, in operation, the writing beam is defocussed when passingthrough the flood gun 7 and is focussed at the storage electrode 3,while the iiooding beam is focussed both at the storage electrode 3A andat the fluorescent screen 2.

The dood gun need not, of course, be constructed Y as above described.For example, the anode could consist of a wall coating on the tube whilethe cathode need not be directly heated but may be indirectly heated.

As will be appreciated the arrangements of the present invention, apartfrom the obvious advantages of having the writing and ood guns mountedon the same axis, allow high resolution to be obtained in writing withthe use of a low voltage writing gun. Furthermore the use yof an axialmagnetic focussing iield enables the flooding beam to be readily evenlydistributed across the storage electrode.

The invention is not, of course, limited to the use of storage tubes inwhich the signals to be stored are used to modulate the writing beam. Itis also applicable, for example, to tubes in which storage is effectedby modulating the collector electrode or the metal grid of the storageelectrode with the signals to be stored, while bombarding the storageelectrode with a writing beam of constant intensity.

We claim:

1. A signal storage tube having a writing gun; a storage electrode; ailood electron gun positioned between the writing gun and the storageelectrode, said ood electron gun being different in area from thestorage electrode and including a grid or mesh cathode of electronemissive material emitting the electrons forming the flood beam andvsoformed as to allow passage therethrough for the electron beam from saidwriting gun; and means for immersing the volume between the loodelectron gun CII fl and the storage electrode in a magneticcollimating-field, the ux density of said magnetic field at the oodelectron gun and at the storage electrode being inversely proportionalto the areas oi the flood electron gun and of the storage electrode,respectively.

2. A tube as claimed in claim l, wherein the cathode of the llood ygunis arranged to be heated.

3. A tube as claimed in claim 1, wherein the cathode of the flood gun isarranged to be directly heated and its grid or mesh comprises an arrayof heater wires coated with an electron emissive material.

4. A storage tube arrangement comprising: a storage tube having, in theorder stated, a writing electron gun mounted on the axis of said tubeand producing a substantially cylindrical writing electron beam, a iloodelectron gun co-axial with said writing gun and -having a cathodeComprising a grid or mesh of electron emissive material emitting theelectrons forming theV lood beam, said grid or mesh having a high ratioof space to conductor width, a secondary electron collector electrodemounted in a plane perpendicular to said axis, a storage electrodeparallel to, and closely spaced from, said collector electrode andcomprising a metallic grid or mesh having deposited thereon on the sidenearer the collector electrode a layer of insulating material, saidstorage electrode being dilferent in area from the liood electron gun,and a fluorescent screen arranged parallel to said storage electrode;means for applying signals to be stored to modulate said writing beam;means, intermediate said writing gun and said dood gun, for deiiectingsaid writing beam; and means for immersing the volume between the floodelectron gun and the'storage electrode in a magnetic collimating ield,the linx density of said magnetic ield at the liood electron gun and atthe storage electrode being inversely proportional to the areas of theood electron gun and of the storage electrode, respectively. 5. Astorage tube arrangement comprising: a storage tube having,V in theorder stated, a writing electron gun mounted on the axis or" said tubeand producing a substantially cylindrical writing electron beam, a floodelectron gun co-axial with said Writing gun and having a cathodecomprising a grid or mesh of electron emissive material emitting theelectrons forming the Hood beam, said grid or mesh having a high ratioof space to conductor widtha secondary electron.collector electrodemounted in a plane perpendicular to said axis, a storage electrodeparallel to, and closely spaced from, said collector electrode andcomprising a metallic grid or mesh having deposited thereon on the sidenearer the collector electrode a layer of insulating material, anaccelerating mesh arranged parallel to and closely spaced from saidstorage electrode, and a fluorescent screen arranged parallel to saidstorage electrode; means for applying signals to be stored to modulatesaid writing beam; means, intermediate said writing and llood guns, fordeecting said writing beam; and means for applying a collimatingimmersing axial magnetic field to said tube.

References Cited by the Examiner UNITED STATES PATENTS 2,661,437 12/53Beckers 313-71 2,748,312 5/56 Beintema 313-68 X 2,824,259 2/58 Smith313-68 X 2,861,207 11/58 Smith et al. 313-68 2,887,597 5/59 Smith et al313-68 2,916,661 12/59 Davis 313-68 X GEORGE N. Wnsrsr, PrimaryExaminer. RALPH G. NILSON, Examiner.

1. A SIGNAL STORAGE TUBE HAVING A WRITING GUN; A STORAGE ELECTRODES; AFLOOD ELECTRON GUN POSITIONED BETWEEN THE WRITING GUN AND THE STORAGEELECTRODE, SAID FLOOD ELECTRON GUN BEING DIFFERENT IN AREA FROM THESTORAGE ELECTRODE AND INCLUDING A GRID OR MESH CATHODE OF ELECTRONEMISSIVE MATERIAL EMITTING THE ELECTRONS FORMING THE FLOOD BEAM AND SOFORMED AS TO ALLOW PASSAGE THERETHROUGH FOR THE ELECTRON BEAM FROM SAIDWRITING GUN; AND MEANS FOR IMMERSING THE VOLUME BETWEEN THE FLOODELECTRON GUN AND THE STORAGE ELECTRODE IN A MAGETIC COLLIMATING FIELD,THE FLUX DENSITY OF SAID MAGNETIC FIELD AT THE FLOOD ELECTRON GUN AND ATTHE STORAGE ELECTRODE BEING INVERSELY PROPORTIONAL TO THE AREA OF THEFLOOD ELECTRON GUN AND OF THE STORAGE ELECTRODE, RESPECTIVELY.